1. Field of the Invention
The present invention relates to oilfield valves. More particularly, the present invention relates to a mud saver valve when installed to prevent the loss of drill fluid during starting operation in deep water wells using a combination of static fluid pressure and flow pressure to open the valve and mechanical spring forces to close the valve.
2. General Background of the Invention
When drill pipe and other tubular strings are lowered into or raised out of a well bore, including, but not limited to, during the drilling of the wellbore, it is quite common, particularly in the oil and gas field, for the drill pipe and other tubular strings to be filled with mud of the type used in drilling techniques. The mud would typically be pumped into the upper end of the drill string after it has been connected to the drill string below it and/or as it is being lowered into a wellbore. As the next joint is added to the drill string, the connection is typically disconnected from the drill string to allow the next section of drill pipe to be connected to the string. When the fluid connection is disconnected, there should preferably to be a mud saver valve in place to retain this fluid and prevent it from flowing out onto the work area and environment. The advantages of using such a valve are well known and include saved mud cost, decreased chances of pollution, and increased safety to rig personnel. To avoid this loss of mud during these types of operations there is needed a mud saver valve which could be positionable just above the drilling bit or just below the bend sub to prevent the loss of drill fluid during starting operation in deep water wells, which reduces the amount of drilling fluid required to start a well and reduces the pollution of the mud bottom with drilling fluid and weighting material.
This invention replaces the original Mud Saver Valve, as disclosed U.S. patent application Ser. No. 12/652,547, noted above, which utilized a pre charged nitrogen dome chamber to feed pre charge pressure to the closing side of multiple pistons that are arranged in an equally spaced circular pattern around the center axis of the valve. The force created by the pre charge pressure acting on the multiple pistons force a slidable sleeve to close the fluid pathway through the valve.
To force the original Mud Saver Valve to open its fluid pathway through the valve, pressure inside the drill pipe at the valve's location in the well bore has to rise above the pre charge pressure of the nitrogen dome plus whatever pressure is required to overcome the friction force of the piston seals. To accomplish this either direct hydrostatic head pressure or the combination of direct hydrostatic head pressure and flow pressure generated by the mud pumps are required.
With the original Mud Saver Valve the amount of pump pressure required to open the valve is a function of the depth of the tool in the well bore. The deeper the tool, the higher the hydrostatic head pressure and the lower the pump pressure required to open the valve.
With the original Mud Saver Valve the valve could be set to open at any particular depth by adjusting the nitrogen pre charge pressure prior to entering the well bore.
The following U.S. patents are incorporated herein by reference:
TABLEU.S. Pat. No./ISSUE DATEPublication No.TITLEDD-MM-YYYY20030102131Mudsaver Valve with retrievable06-05-2003inner sleeve.20050189144Mud Saver Valve09-02-200520050236191Drill String Valve Assembly10-27-200520010037900Mud Saver Kelly Valve11-08-200120070039759Mud Saver Valve02-22-20077,048,079Mud Saver Valve05-23-20066,053,191Mud-Saver Valve04-25-20006,640,824Mud Saver Kelly Valve11-04-20036,662,886Mudsaver Valve with Dual Snap12-16-2003Action